For example, Patent Document 1 discloses a conventional technique used for effectively utilizing communication links by reducing the amount of data that is revoked in a packet discarding process. According to the conventional communication method described in Patent Document 1, a base station control device generates wireless segments by dividing a received packet into segments each having a length corresponding to the unit of communication used on the wireless communication link. The base station control device then specifies information regarding re-transmission control into the headers of all the generated wireless segments and transmits the wireless segments to a base station. The base station generates predetermined transfer frames (wireless transfer blocks) from the wireless segments that have been received from the base station control device and transmits the generated wireless transfer blocks to a mobile station. Also, the base station determines the number of times of re-transmission of each of the wireless transfer blocks in such a manner that the closer to the end of the packet the wireless segment from which the wireless transfer block has been generated is positioned, the larger is the number of times of re-transmission. In the case where the base station fails to properly receive any one of the wireless transfer blocks within the determined number of times of re-transmission, the base station discontinues re-transmission of such a wireless transfer block and discards the wireless segment corresponding to the wireless transfer block and all the wireless segments following that wireless segment.
In other words, according to the conventional communication method described in Patent Document 1, with respect to a packet in which many of the wireless transfer blocks have already been delivered, the number of times of re-transmission for each of the remaining wireless transfer blocks that have not yet been delivered is specified to be a larger value. As a result, it is possible to lower the possibility of having the transmission of the wireless transfer blocks discontinued due to the number of times of re-transmission exceeding the determined value and the possibility of the mobile station being unable to reproduce the original packet and wasting the wireless transfer blocks that are already acknowledged as having been delivered. Thus, the wireless communication link (frequency) is effectively utilized.
To ensure that a handover is performed between base stations without missing any data, in the case where a packet fails to be delivered between a handover-origin base station and a mobile station, the packet needs to be transmitted again between a handover-destination base station and the mobile station. In this situation, however, if many of the wireless transfer blocks within the packet have already been delivered, transmitting the packet again between the handover-destination base station and the mobile station leads to a problem where the wireless transfer blocks that are already acknowledged as having been delivered are wasted and the wireless communication link (frequency) is thus wasted. In addition, it is also necessary to ensure that the downstream packet that has failed to be delivered is transferred from the handover-origin base station to the handover-destination base station.
For example, Patent Document 2 discloses a conventional technique to solve these problems. According to the technique disclosed in Patent Document 2, the actual execution of a handover is delayed until the reproduction of a packet is completed on the reception side. Thus, it is possible to lower the possibility of having short packets discarded, to prevent degradation of the utilization efficiency of the frequency as much as possible, and to prevent the increase of delays as much as possible. In other words, according to the conventional technique described in Patent Document 2, it is possible to avoid wasting the wireless communication link by executing the handover after the packet has been completed.
Patent Document 1: Japanese Patent Application Laid-open No. 2005-27167
Patent Document 2: Japanese Patent Application Laid-open No. 2000-92542